WELL; Cancer Risk To Children Is Found In CT Scans

By DENISE GRADY

Published: June 7, 2012

CT scans in children can cause small but significant increases in the risk of leukemia and brain cancer, a new study finds.

Researchers say the results do not mean that CT scans should be avoided entirely - they can be vitally important in certain situations, like diagnosing severe head injuries - but that the test should be performed only when necessary, and with the lowest possible dose of radiation.

CT, or computed tomography, scans take X-rays from various angles and combine them to create cross-sectional images, and they involve much more radiation than traditional X-ray techniques. Concern about potential harm from the scans has grown as their use has climbed steeply; at least four million children a year receive scans in the United States, and researchers estimate that a third of the scans are unnecessary or could be replaced by safer tests like ultrasound or magnetic resonance imaging, which do not use radiation.

The new study, published online on Wednesday in The Lancet, a British medical journal, is based on the records of nearly 180,000 children who had scans from 1985 to 2002 in Britain. There were 74 cases of leukemia and 135 cases of brain cancer in the group. The authors estimated the radiation doses and found that the more scans the children had and the more radiation they received, the higher their risk.

Children under 15 who had two or three scans of the head had triple the risk of brain cancer compared with the general population, the researchers found, and 5 to 10 scans tripled the risk of leukemia. But the baseline risk is extremely low - 4.5 cases of leukemia per 100,000 people under 20, and 3.5 cases of cancer of the brain or central nervous system - so that even tripled, it remains small.

''The basic message for childhood cancers is that they are rare,'' said Mark S. Pearce, the first author of the study, from Newcastle University and the Royal Victoria Infirmary.

In response, the American College of Radiology issued a statement urging parents not to refuse needed CT scans, especially for potentially life-threatening conditions like head and spine injuries, pneumonia complications and chest infections. But the organization also lists conditions for which CT should not be the first choice; one is suspected appendicitis in children, for which the group recommends that ultrasound be used first, followed by CT only if the ultrasound is equivocal.

The Lancet study has limitations: It is observational, meaning that the researchers just looked at what happened to patients without picking them at random to be treated or not, which provides more solid evidence but cannot be justified ethically in studies of radiation. In this case, all the children received scans; there is no unexposed control group. And the researchers say they do not know why the children had the scans, though they excluded those whose cancer diagnosis came so soon after the CT scan that it may have been present before the scan was performed.

An editorial in the same issue of the journal notes that Dr. Pearce's findings, based on data from actual patients, support earlier risk estimates based on comparisons of the radiation dose from CT scans to the doses received by survivors of the atomic bombing of Japan, who had an increased risk of cancer. The editorial, by Dr. Andrew J. Einstein of Columbia University Medical Center, said that at least a dozen other research groups around the world were studying or planning to study CT effects on children.

A major study warning of CT risks to children, based on the Japanese exposure, was published in 2001; it predicted that of the 600,000 children under 15 who were having head and abdominal scans in the United States each year, 500 might ultimately die of cancer caused by the CT radiation.

The first author of that study, David Brenner, director of the Center for Radiological Research at the Columbia University College of Physicians and Surgeons, said that young people were often given CT scans to diagnose kidney stones, appendicitis and dental problems, and that some of those scans could have been avoided by using other methods, like ultrasound or conventional X-rays.

''There's been a lot of emphasis on reducing the dose'' in the decade since, Dr. Brenner said. ''That's really good. Industry got on board.''

But, he emphasized, more work is needed to make sure doctors order the scans only when needed.

This is a more complete version of the story than the one that appeared in print.

PHOTO: A study says CT scans for children should use the lowest possible dose of radiation. Above, a scanner in Birmingham, England. (PHOTOGRAPH BY CHRISTOPHER FURLONG/GETTY IMAGES)